Controller for a handpiece



FIG. 1 is a front elevation view of a controller for a handpiece, showing my claimed design;

FIG. 2 is a rear elevation view thereof;

FIG. 3 is a left side elevation view thereof;

FIG. 4 is a right side elevation view thereof;

FIG. 5 is a plan view thereof; and,

FIG. 6 is a base view thereof. 

The ornamental design for a controller for a handpiece, as described and shown. 